Thes is deals with the construction, protective circuits and lifetime of lithium ion batteries intented for powering electric bicycles. The entire battery is composed of Li-ion cells with the designation 18650 from Sanyo company, which are connected via series-parallel combination. Because of the series connection of the cells, it is necessary to add protective circuit to each cell to prevent overcharging or deep discharging, on which Li-ion cells are very sensitive. Absence of these circuits could cause irreversible damage to the entire battery pack. Life of Li-ion cells depends on many aspects. These aspects have an influence on the electric bicycle itself. They have an impact on the range and the number of charging and discharging cycles against the considerably high price of the battery.